The nice thing about Kochiku is that it is a free open source project whereas CircleCI is a paid hosted solution. If you have hardware available to use as workers on then Kochiku is free to use. There is a real cost to the time required to setup and maintain Kochiku but, at scale, within a larger company, this route can make sense.

I am sure CircleCI takes security very seriously but it also nice (and a requirement for certain companies) that with a self hosted CI server, that your source code does not leave the company.